The establishment of functional neuronal circuits relies on the formation of excess synapses, followed by the elimination of inappropriate connections. Although the stabilization of presynaptic inputs is critical for the development and maintenance of functional circuits, the signals that regulate presynaptic stability are not known. Our preliminary studies suggest that synapse formation in cortical cultures is highly dynamic and involves the stabilization of a subset of synapses in a backdrop of a high rate of synapse formation and elimination. During the peak of synaptogenesis, only about 50% of putative synapses are stable over an hour. We have found that presynaptic stability is strongly correlated with the presence of postsynaptic AMPA but not NMDA receptors. We have identified LRRTM2 as a GluR2-interacting transmembrane protein that affects synapse stability. Based on our preliminary studies we hypothesize that a GluR2- LRRTM2 complex functions as a retrograde signal to regulate presynaptic stability. The specific aims of this proposal are: Aim 1: To determine whether gain or loss of GluR2 receptors affects synapse stability, and to identify the domains of GluR2 that mediate this effect Aim 2: To identify the domains of GluR2 and LRRTM2 that mediate their interaction and to identify the mechanism by which LRRTM2 is recruited to synaptic sites Aim 3: To determine the role of GluR2-LRRTM2 interactions in regulating presynaptic stability and synaptic function These experiments will provide important insights into the mechanisms that regulate synase formation and stability. These mechanisms are likely to be disrupted in neurological diisorders such as Rett Syndrome, Autism, and Alzheimer's disease that are characterized by loss of synapses and may suggest approaches for therapeutic intervention. PUBLIC HEALTH RELEVANCE: The goal of this project is to understand the molecular mechanisms that regulate the formation of synaptic connections in the brain during development. Several childhood neurological disorders, such as Autism, Rett Syndrome, and X-linked mental retardation are characterized by defects in synaptic connectivity. The findings of this project should guide efforts to better understand and develop therapeutic strategies for these disorders.